An OLED (organic light emitting diode) display device is a self-luminous display. Compared with an LCD (liquid crystal display), an OLED display device does not require a backlight, and thus a thickness of the OLED display device is thinner than that of the LCD. Besides, OLED display devices are increasingly applied to a variety of high performance display fields for their various advantages such as great brightness, low power consumption, wide viewing angle, fast response, wide operation temperature range and the like.
The luminescence mechanism of the OLED devices is that, under an action of an applied electric field, electrons and holes are injected into an organic light-emitting material from a cathode and an anode respectively, electrons and holes migrate, recombine and attenuate in the organic light-emitting material to emit light. Because the electron affinity of the organic light-emitting material is far smaller than that of a metal material or an inorganic material, a work function of the cathode material must be low enough to meet the requirement of injecting electrons into the organic light-emitting material efficiently. Currently, the cathode of the OLED device is generally made of a metal or a metal alloy with a low work function.
However, in the case that the cathode of the OLED device is made of a metal or a metal alloy, on the one hand, the metal or the metal alloy tends to deteriorate in the atmospheric environment, so that the quality of OLED devices are degraded; on the other hand, the cost of the metal or the metal alloy is high.